In image forming methods such as an electrophotographic method, an electrostatic photographic method, and electrostatic printing method, toners are used to develop latent electrostatic images.
A toner or a colored resin powder for developing latent electrostatic images in electrophotography and the like is formed at least from a binding resin and a colorant. Usually, the toner or colored resin powder is prepared by melt kneading a mixture having at least the aforementioned materials in a kneading apparatus, cooling and solidifying, and then pulverizing and classifying the solidified material to adjust it to a predetermined particle size.
Presently various property values of toners or colored resin powders, after their particle size has been adjusted to a predetermined level, are improved by adding various additive(s), e.g., with the object of improving flowability index.
Customers require image forming systems that can provide high-sensitivity and high-quality images, and toners are accordingly required to have decreased softening point and reduced particle size.
Further, mechanical pulverizing apparatuses such as shown in FIG. 4 have been mainly used in recent years because they discharge less carbon dioxide than conventional airflow pulverizers and place a small load on environment.
However, the problems associated with such apparatuses include wear of rotor or stator and reduced production capacity caused by contact with the material to be pulverized during pulverizing.
Patent Literature 1 describes a mechanical pulverizing apparatus containing a rotor and a stator that is held at a fixed distance from the rotor surface and disposed around the rotor, where a constant gap between the rotor and stator forms an annular space, this apparatus having a surface treated layer at least on either the rotor surface or the stator surface, this surface treated layer being obtained by plating with a chromium alloy having chromium carbide. The problem associated with such mechanical pulverizing apparatus is that microcracks appear in a long-term use making it impossible to use the apparatus.
Patent Literature 2 describes a toner manufacturing method by which material to be pulverized that has a large particle diameter and has a coarse pulverized product that has been recycled is introduced for pulverizing into a mechanical pulverizing apparatus having a rotor and a stator that is held at a fixed distance from the rotor surface and disposed around the rotor, coarse particles and overpulverized particles are removed by classification from the pulverized material, and the remaining pulverized material with a predetermined particle diameter is introduced into a surface modification apparatus using mechanical impact force for surface modification, wherein a surface of an impact force imparting member of the surface modification apparatus has a chromium plated layer having chromium carbide. However, because the chromium plated layer is not an alloy containing Cr as the main component and having other elements such as Mg, Al, Si, Ti, Mn, Fe, and C, wear resistance thereof is not always sufficient.
The inventors have earlier suggested (in particular, see Patent Literature 3) providing a coating for improving wear resistance on the surface of an impeller constituting a classification rotor of the toner manufacturing apparatus, but this toner manufacturing apparatus is a fluidized bed pulverizing apparatus rather than a mechanical pulverizing apparatus. Further, the coating designed to improve wear resistance is Nickel Teflon (trade name) and is not an alloy containing Cr as the main component and having other elements such as Mg, Al, Si, Ti, Mn, Fe, and C.
As shown in FIG. 1, the plated layer starts peeling from the crack initiation locations.
Wear generated in the case illustrated by FIG. 1 is apparently chipping wear.
Further, because metal particles are larger than toner particles, the metal particles cause cracking when they penetrate into joint portions, thereby easily inducing chipping wear.
To repair the structure, an extremely complex process has to be used in which the original coating film is stripped completely and the entire surface is cleaned and recoated.    [Patent Literature 1] Japanese Patent Application Laid-open (JP-A) No. 2003-173046    [Patent Literature 2] Japanese Patent Application Laid-open (JP-A) No. 2005-195762    [Patent Literature 3] Japanese Patent Application Laid-open (JP-A) No. 2005-177579